The present invention relates to a method for putting color to glass by laser irradiation. There are known the following methods for putting color to glass by laser irradiation.
An irradiation of an inside of a glass with a convergent ultraviolet laser can form a color center (e.g., non-bridging oxygen hole center) due to two-photon absorption. The light absorption by this color center provides a glass with a brown color. Thus, it is possible to put desirable marks on glass by laser beam irradiation.
Furthermore, an irradiation of an inside of a glass with a convergent ultraviolet laser can form a laser shot trace (refractive index modified portion) having a refractive index different from that of the surrounding glass. Although the resulting refractive index modified portion is transparent, it is seen as having a white color such as papermark (watermark) due to its modified refractive index as compared with that of the surrounding glass. Thus, it is also possible to put white marks on glass by laser beam irradiation.
Still furthermore, an irradiation of an inside or surface of a glass with a convergent ultraviolet laser can form cracks or defects to provide a white color. Thus, it is also possible to put white marks on glass by laser beam irradiation.
In particular, an irradiation of the surface of a silver-doped glass with a convergent ultraviolet, visible or infrared laser generates silver fine particles to put a brown, yellow or gold color on the glass.
Hitherto, the laser beam irradiation for putting color on glass has been conducted by using a single laser beam. Therefore, it has been necessary to take much time to put complicated marks by such a single laser beam irradiation.